Spatial and temporal patterns of surface–atmosphere energy exchange in a dense urban environment using scintillometry

Crawford, Ben; Grimmond, Sue; Ward, Helen C.; Morrison, William; Kotthaus, Simone

doi:10.1002/qj.2967

Cited by 25 publications

(30 citation statements)

References 53 publications

(94 reference statements)

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“…For this reason Q H is not strongly correlated with building or vegetation fraction, as it is in other cities e.g. Basel (Christen and Vogt 2004), Swindon (Ward et al 2014), London (Crawford et al 2017). As highlighted by Ward et al (2015b), there is still a need for long-term scintillometer measurements of sensible and latent heat fluxes in urban areas that capture both the seasonal and inter-annual variability.…”

Section: Discussionmentioning

confidence: 99%

“…To isolate anthropogenic and weather influences on Q H , Crawford et al (2017) applied the conditional sampling for their dataset. With the aid of high-resolution radar data on precipitation they were able to distinguish 'wet' and 'dry' days.…”

Section: Dependence Of Turbulent Sensible Heat Flux On Wind Directionmentioning

confidence: 99%

“…Kotthaus and Grimmond (2014a) showed that Bowen ratio can be reduced even 12 h after the rain. Therefore we decided to treat all observations from periods up to 12 h after the precipitation, as cases with wet surface, even though Crawford et al (2017) used only 3 h threshold for London. The application of small threshold for our dataset will make further analysis impossible, due to low data availability.…”

Section: Dependence Of Turbulent Sensible Heat Flux On Wind Directionmentioning

confidence: 99%

“…The SAS instrument provides fluxes averaged over relatively short paths (up to 250 m), and to obtain fluxes representative of larger areas, a large-aperture scintillometer (LAS) should be used. The LAS instrument has been used in a number of cities, e.g., Marseille (Lagouarde et al 2006), London (Wood et al 2013a), Helsinki (Wood et al 2013b), Łódź (Zieliński et al 2013), Swindon (Ward et al 2014), and Changzou (Zhang and Zhang 2015), London (Crawford et al 2017). More recently, Ward et al (2015a, b) used a system consisting of a LAS intrument and a microwave scintillometer to measure the sensible and latent heat fluxes simultaneously over the city of Swindon in the UK.…”

mentioning

confidence: 99%

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Long-term Turbulent Sensible-Heat-Flux Measurements with a Large-Aperture Scintillometer in the Centre of Łódź, Central Poland

Zieliński

Fortuniak

Pawlak

et al. 2018

Boundary-Layer Meteorol

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We investigate the area-averaged sensible heat flux (Q H ) obtained with a scintillometer along a 3.1-km path length over the city centre of Łódź, Central Poland. The annual cycle of Q H peaks in June but is lower by the middle of summer. In winter, due to a large amount of anthropogenic heat input, Q H remains positive all day long, with positive nighttime fluxes also found during months with frequent cold advection, e.g., June 2010. In the diurnal cycle of this flux, several features specific to urban areas are seen: the peak shifts 1-2 h after noon, the heat flux turns from positive to negative 1-2 h after sunset. In Łódź Q H was observed during inflow from the north and north-west, i.e. from the city centre. As this area is mostly covered with impervious materials, most of the heat exchanged between the ground and the overlying air is in the form of sensible heat flux. Under the conditions of inflow from the east and south-east, the maximum heat flux is approximately 100 W m −2 lower than during the inflow from the city centre, since more vegetation exists to the east and south-east of the scintillometer path. Cold and warm advection are found to be a vital factor in the observed heat-flux variability in the centre of Łódź.

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Section: Discussionmentioning

confidence: 99%

Section: Dependence Of Turbulent Sensible Heat Flux On Wind Directionmentioning

confidence: 99%

Section: Dependence Of Turbulent Sensible Heat Flux On Wind Directionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Long-term Turbulent Sensible-Heat-Flux Measurements with a Large-Aperture Scintillometer in the Centre of Łódź, Central Poland

Zieliński

Fortuniak

Pawlak

et al. 2018

Boundary-Layer Meteorol

View full text Add to dashboard Cite

show abstract

“…A full description of the instrumentation and data processing details for the scintillometer network can be found in Crawford et al . ().…”

Section: Methodsmentioning

confidence: 97%

Variability of urban surface temperatures and implications for aerodynamic energy exchange in unstable conditions

Crawford

Grimmond

Gabey

et al. 2018

Quart J Royal Meteoro Soc

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Sensible heat flux (Q H ) is a critical driver of surface and boundary layer meteorological processes, especially in urban areas. Aerodynamic resistance methods (ARM) for modelling Q H are promising because, in principle, all that is needed is surface temperature (T 0 ), air temperature (T A ) and an aerodynamic resistance term (r H ). There are significant challenges in urban areas, however, due to uncertainties in satellite-derived land surface temperatures (LST), logistical challenges in obtaining high-resolution air temperatures, and a limited understanding of spatial and temporal variability of r H and associated variables (e.g. thermal roughness length). This work uses an extensive LST dataset covering 6 years (2011)(2012)(2013)(2014)(2015)(2016) in central London and a long-term in situ observation network to analyse the variability of LST and r H variables. Results show that LST is spatially correlated with building and vegetation land cover with coherent thermal structures at length scales less than 500-1,000 m. Additionally, satellite-observed LST varies with average building height (up to 10% cooler in areas with tall buildings). The r H term and associated variables are observed to vary on daily and seasonal cycles, and findings are used to model Q H using five variations of an ARM-based approach on a 100 m pixel basis. Modelled Q H is compared to observations from three scintillometer paths and an eddy covariance flux tower. We find generally good agreement between observations and models, although there is uncertainty in all methods (mean absolute error ranges from 58.1-129.3 W/m 2 ) due to the challenges involved in determining high-resolution meteorological and surface inputs, particularly LST and friction velocity (u * ). Additional complexity in evaluating modelled Q H arises from anthropogenic heat sources: long-term tower-based observations show that T A and the radiometer-derived T 0 are warmer during working weekdays than non-working days (up to 0.7 • C) and that there is an observed lag (2-3 hr) between energy consumption and the observed warming and modelled Q H .

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Atmospheric boundary‐layer characteristics from ceilometer measurements. Part 2: Application to London's urban boundary layer

Kotthaus

Grimmond

2018

Quart J Royal Meteoro Soc

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Long-term measurements of mixed layer height (Z ML ) are possible with advances in detecting Z ML based on Automatic Lidars and Ceilometers (ALC) observations. Six years of ALC measurements in central London are analysed using the CABAM ("Characterising the Atmospheric Boundary layer (ABL) based on ALC Measurements") algorithm which provides Z ML and an ABL classification by cloud cover and type. The boundary-layer dynamics are shown to respond to day-length, cloud cover and cloud type. Seasonal median daily maxima range from 707 m (stratiform clouds) to 1704 m (days with convective boundary-layer clouds following a clear night). A common approach to ABL classification and clear definition of key Z ML -indicators can facilitate inter-city comparison. A simple parametrisation based on empirical coefficients derived from the London measurements is proposed to generalise the description of diurnal and seasonal variations in Z ML , including cloud conditions. This has the potential to aid improved understanding of the complex relations between surface air quality and boundary-layer dynamics. KEYWORDS

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Spatial and temporal patterns of surface–atmosphere energy exchange in a dense urban environment using scintillometry

Cited by 25 publications

References 53 publications

Long-term Turbulent Sensible-Heat-Flux Measurements with a Large-Aperture Scintillometer in the Centre of Łódź, Central Poland

Long-term Turbulent Sensible-Heat-Flux Measurements with a Large-Aperture Scintillometer in the Centre of Łódź, Central Poland

Variability of urban surface temperatures and implications for aerodynamic energy exchange in unstable conditions

Atmospheric boundary‐layer characteristics from ceilometer measurements. Part 2: Application to London's urban boundary layer

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